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Continental TurboProp crash inbound for Buffalo

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Continental TurboProp crash inbound for Buffalo

Old 20th Feb 2009, 18:50
  #761 (permalink)  
 
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Surely the pusher itself distinguishes itself from say, a tail-stall stick force, by a bright light or horn warning/annunciation of some type, so that there can be no doubt what is causing the stick-force?

I can see why the extent of sim training is starting to come into focus...
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Old 20th Feb 2009, 18:54
  #762 (permalink)  
 
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Quote from microCruzer

I definitely agree with all of you stating that a power increase could be neglected due to some distraction but I have much harder to see that happening while changing flaps configuration, twice (to flaps 5 and to flaps 15) since in my mind this more or less automatically triggers speed awareness. What do you think?
--Well said.

Can someone tell me how the increase in ref speed resulting from deice selection affect the stick shaker versus pusher.
D777 mentioned 2 degree or so difference in AOA between the 2 events. Does the deice change shaker and pusher AOA both, if so, both equally?
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Old 20th Feb 2009, 19:35
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T-tails and Deep stalls

There's been no comment that I've seen so far to the fact that T-tails have special handling characteristics in extreme nose up situations, where the aircraft can become uncontrollable. Could this have happened when the AP was released? See T-tail and deep stall at Stall (flight) - Wikipedia, the free encyclopedia.

Last edited by Tfor2; 20th Feb 2009 at 20:07. Reason: made external link
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Old 20th Feb 2009, 19:52
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Two points which have been made before and possible stand repeating.

Tail stalls happen because the disturbed air from the ice build up cause a low pressure pocket of disturbed air on the lower surface of the horizontal stabiliser. When this bubble reaches the elevator it pulls it forward.

The Q400 has an all powered tail. The elevators are not moveable by aerodynamic forces at all. only by the hydraulic rams. All you have at the front end is a spring bias to feel the forces.

Secondly, the Q400 has a fair amount more power available than most if not all commercial turboprops. Firewalling or even selecting the detent when MCR would have been indicating on the ED would give a massive amount of lift, up pitching moment and also left yaw. Performing go-around is the sim when trimmed to 20 kts higher is still a fight, let alone trimmed to the stall...... Countering a lot of left yaw with too much right rudder, while just at the stall, with loads of power and a pitch up force sounds just like a classic spin entry manoever to me.....

However, the actual sequence of control movements will come out in the report and before drawing conclusions on this specific event, we should wait for that.

Personally, I'm more than happy to go fly a Q400 anyday.
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Old 20th Feb 2009, 20:00
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Did they just think they had icing?

Apologies if this has been mentioned before.

I've just watched the video on tailplane icing. If the pilots were concerned about icing and they knew about tailplane icing, then what would their reaction be if after extending flaps, the stick started to shake? And then the forward force on the stick increased?

Just an idea.
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Old 20th Feb 2009, 20:19
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From looking at these 4 NTSB reports (which I posted earlier), here's another possibility for what happened to flight 3407. I seem to remember someone else may have speculated about this earlier.

LAX06IA076
DCA01MA031
DCA97MA017
DCA93IA027

If the autopilot was set to ALT HLD (for 2300 ft), AND the airframe and/or wings were accumulating ice, it could have happened like this.

As the aircraft descended and slowed, then leveled at ALT HLD at 2300ft, ice buildup could have added to the airframe drag, and loss of lift from the wing. Then as the pilots made power adjustments (to around 134kts +/-) for flaps 5, then the landing gear, then flaps 15, the autopilot could have been adjusting the stabilizer trim to a higher AOA (more nose up) to compensate for the airframe drag and loss of lift at that airspeed, to maintain 2300ft.

As the flaps were transitting to 10 degrees, the combination of airframe drag, loss of lift and airspeed, along with the increased AOA necessary to maintain 2300ft, may have triggered the stick shaker and pusher, which disconnected the autopilot. At that point, the stabilizer trim may have been adjusted significantly nose up, compensating for the drag and lift loss to maintain that altitude. This might explain the immediate 31 degree nose pitch up, after the autopilot disconnected. And if there was ice accumulated on the wings (beyond the boots) and on the airframe, it would have made the stall worse, and recovery that much more difficult.

However to counter this theory, the NTSB has said they did not hear significant trim motor sounds on the CVR. That said, the FDR would probably give a more complete picture of this.

Last edited by Flight Safety; 20th Feb 2009 at 20:30. Reason: To make the language more clear.
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Old 20th Feb 2009, 20:56
  #767 (permalink)  
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Deano posted:

the Q400 stick pusher operates with 36kg of stick push force, it requires 36kg of reverse pressure to stop this push, and then a further 30kg of constant pressure to override the pusher clutch.
I'm a little puzzled by your description of these forces, not because I know anything about the Q's systems, but because you seem to be saying that there has to be considerable pilot input just to get back to square one. A summing of those two forces in fact.

I had assumed that the stick is totally free after a normal and uninterrupted push, but I don't know. So therefore it was specifically the time that the pusher took to release the force, that I was referring to, based on my assumption. On some jet transports it was released as soon as the push completed and the vertical flow on the veins returned to an acceptable figure.
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Old 20th Feb 2009, 21:09
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NTSB

Sorry I can't see how to quote anymore but Flight Safety pointed out the responses from the interested parties.

NTSB (maybe) - "We've been discussing icing for years..."

They've been discussing - and writing to the FAA - about pilot fatigue for years too but nothing changes. So, I will watch with interest to see what comes out of this re training.

Anyone who's flown for a regional shoestring operation will know that training can be pretty minimal, as others have already said. The tragedy here is that not only have 50 lives been lost but 2 of those were pilots at the beginning of their careers who would in all probability gone on to be top class experienced professionals had the training they received been commensurate with the responsibilities they were given.

Obviously I speculate but it has an awful ring of familiarity to me.
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Old 20th Feb 2009, 21:34
  #769 (permalink)  
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Obviously I speculate but it has an awful ring of familiarity to me
And so does the ring of kicking tin.
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Old 21st Feb 2009, 00:22
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It would APPEAR that the First chain in this accident happened far before GS intercept , HOWEVER, it might be that the Biggest hole in the cheese is the Failure to maintain PROPER airspeed ! YES, we need to fix all the other "holes" But , we cant forget about human error ( 2 ) concerning a very Basic flying skill ( maintaining airspeed ) Even some of the big holes are difficult to prevent !
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Old 21st Feb 2009, 00:27
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789 Flight Safety

As I see it ,if Autopilot kicks out because of stick push, and/or of running out of trim to hold the nose up there cannot be a further pitch up of some 30 degrees caused merely by nose up trim . Something else must have been added at the same time.
I feel that deep stall is unlikely because this is not a swept wing.
We need a precise time line of events.
Did flaps stop at 20 degrees or did they go from 25 back to 20, which might move Cof P forward a little?
I see it being plausibly suggested that an unrecognised stick push could have been mistaken for Tail ice stall with an instantaneous decision called for to pull or to push.(I was caught once with iced up ASIs , Altimeters and Vsi in a similar coffin corner situation, in the dark ,with buffet; we didnt know if it was compressibiliy or normal stall, fortunately we had height and time to discuss and find other clues)
But I also understand from a recent comment here that the aircraft may have after all been intercepting the ILS from the wrong side , with associated notamed problems
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Old 21st Feb 2009, 00:29
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If the crew is to be blamed

I do hope that the training department and bombardier can both prove THEY TOLD THE PILOTS THAT THE Q400 was not likely to get TAILPLANE STALL.

I've made comments on training, certification, evaluation and the like. IF you blame the pilots and DON"T blame the training and the like, you have a big problem.

Tell me the crew had heard, "Q400's don't tailplane stall" and you can blame them for anything. But if they haven't...ouch to the training department...the FAA too.

I will also say this...your right hand belongs on the throttles, your left on the yoke during critical phases of flight...this plane was in a critical phase of flight. (captain in this example)
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Old 21st Feb 2009, 00:33
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As the flaps were transitting to 10 degrees, the combination of airframe drag, loss of lift and airspeed, along with the increased AOA necessary to maintain 2300ft, may have triggered the stick shaker and pusher, which disconnected the autopilot. At that point, the stabilizer trim may have been adjusted significantly nose up, compensating for the drag and lift loss to maintain that altitude. This might explain the immediate 31 degree nose pitch up, after the autopilot disconnected.
As an aircraft with positive static longitudinal stability (like the DHC-8-400) decelerates, if no control inputs were made, the nose would fall. The autopilot applies increasing aft stick commands to hold level flight. The autopilot will command the pitch trim to run to reduce the sustained control force that it is holding. The result is that the autopilot is always slightly slow to move the trim, and the control force is never completely trimmed out. If the autopilot disconnects, and nothing else has changed, the nose will fall slightly.

There has to be another reason for the increase in pitch attitude to 31 degrees nose up. It was probably due to the sum of pilot aft control input, and the pitching moment due to the large change in power that he made. I am told that the FDR on the -400 records the force the pilot puts on the controls, so it should be possible to eventually learn what the actual pilot control inputs were.
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Old 21st Feb 2009, 00:33
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Did flaps stop at 20 degrees or did they go from 25 back to 20, which might move Cof P forward a little?
I believe the NTSB has stated that the flaps were never at more than 10 degrees.
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Old 21st Feb 2009, 00:40
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I do hope that the training department and bombardier can both prove THEY TOLD THE PILOTS THAT THE Q400 was not likely to get TAILPLANE STALL.
I don't know what info the airline training department passed on to the pilots, but the Bombardier systems description info should quite clearly describe that the aircraft has a powered irreversible flight control system for the elevator. Thus the crew should have been aware that changes in air loads on the elevator could not cause the controls to suddenly move forward. If the airline simply showed the NASA training material with the Twin Otter tail plane stall video, without explaining the important ways the -400 differed from the Twin Otter, then they did a shoddy job, in my opinion.
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Old 21st Feb 2009, 04:44
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From an article in Tampa Bay Online:

Renslow, an Iowa native, developed a passion for flight when he was 5 years old. He had several careers but began his piloting career in 2003 as a pilot for Gulf Stream International Airlines.
As a pilot, he had no prior accidents, incidents or enforcements, according to Roland Herwig of the Federal Aviation Administration. He joined Colgan Air, which operated the flight, on Sept. 9, 2005,
Gulfstream International, another Continental Connection feeder airline based in Florida, only uses Beech 1900s so it looks like the captain moved up from those to Saab 340s and then to Q400s.
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Old 21st Feb 2009, 08:26
  #777 (permalink)  
 
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And so does the ring of kicking tin.

No it doesn't. A far less familiar sensation. Decry it all you like but there are sections of the industry where the problem is endemic. I've seen it & ex colleagues still report it.
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Old 21st Feb 2009, 08:49
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I agree with khorton that there is no obvious reason for getting an out of trim condition at autopilot disconnect. The trim input purpose is to trim the a/c for the actual conditions. If I disconnect the autopilot at Vref just before landing (AoA about 6 degrees) I do not get a lot of forces in my hand.
Then the question is how is the application of possibly max power (firewall) affect the rotation along the y-axis. I do not remeber this from the Q400 simulator, I do remember that pulling the PLs to disc after landing generates a pitch down movement. This depends on drag from the propellers through the propeller axis but there is also effect due to removing the propeller generated air-flow over the wings. This is no proof that it is the opposite when doing the opposite since for instance after landing the main gears are also generating a moment.

Anyone more recent on the Q400 has an idea of what rotational forces there are when applying max power from a trimmed idle position?
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Old 21st Feb 2009, 09:42
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With reference to this article:

Quiet revolution-25/04/2000-Flight International

Could the reason for the addition of the lower fuselage ventral strakes have been a factor? The ref. article explains the reason the strakes were added:

"During the Q400's development testing the six bladed propeller slipstream was found, during side-slips at V2, to wrap round the fuselage and impinge on the opposite side of the fin and rudder. This tendency was cured by fitting the two long ventral strakes under the fuselage's rear half."

The same article also describes maximum rudder deflection is restricted to 12 degrees with flaps up, but with flaps 5 or greater it increases to 18 degrees.

The side-slip at V2 most likely relates to single engine operation when reading the article but would the ventral fins have any effectiveness with the engines/propellers at high power settings with the aircraft at low speed and a pitch of 31 degrees? The accident aircraft had 10 degrees of flap which would result in 18 degrees of maximum rudder deflection. Any flow wrapping around the opposite side of the rudder may have resulted in the aircraft to yaw in the opposite direction than anticipated by the crew?

One more question related to this article: "All Q400 take-offs have to be brakes-off, rolling start." No explanation is given as to why, do any Q400 drivers know why this is the case?

Thanks,

Green-dot
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Old 21st Feb 2009, 11:15
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FAA Directive FAA-2009-0130

Is this relevant in this case?

FAA directive FAA-2009-0130 issued February 20 2009.

Quote
[Docket No. FAA-2009-0130; Directorate Identifier 2008-NM-225-AD;
Amendment 39-15817; AD 2009-04-11]
RIN 2120-AA64


Airworthiness Directives; Bombardier Model CL-600-2B19 (Regional
Jet Series 100 & 440) Airplanes

AGENCY: Federal Aviation Administration (FAA), Department of
Transportation (DOT).

ACTION: Final rule; request for comments.

-----------------------------------------------------------------------

SUMMARY: We are adopting a new airworthiness directive (AD) for the
products listed above. This AD results from mandatory continuing
airworthiness information (MCAI) originated by an aviation authority of
another country to identify and correct an unsafe condition on an
aviation product. The MCAI describes the unsafe condition as:

The heating capability of several Angle Of Attack (AOA)
transducer heating elements removed from in-service aircraft have
been found to be below the minimum requirement. Also, it was
discovered that a large number of AOA transducers repaired in an
approved maintenance facility were not calibrated accurately.
Inaccurate calibration of the AOA transducer and/or degraded AOA
transducer heating elements can result in early or late activation
of the stall warning, stick shaker and stick pusher by the Stall
Protection Computer (SPC).
* * * * *
The unsafe condition is reduced controllability of the airplane.
This AD requires actions that are intended to address the unsafe condition described in the MCAI.

...

SUPPLEMENTARY INFORMATION:

Discussion

The Transport Canada Civil Aviation (TCCA), which is the aviation
authority for Canada, has issued Canadian Airworthiness Directive CF-
2008-35, dated December 22, 2008 (referred to after this as ``the
MCAI''), to correct an unsafe condition for the specified products. The
MCAI states:

The heating capability of several Angle Of Attack (AOA)
transducer heating elements removed from in-service aircraft have
been found to be below the minimum requirement. Also, it was
discovered that a large number of AOA transducers repaired in an
approved maintenance facility were not calibrated accurately.
Inaccurate calibration of the AOA transducer and/or degraded AOA
transducer heating elements can result in early or late activation
of the stall warning, stick shaker and stick pusher by the Stall
Protection Computer (SPC).
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